A purpose of a brush in an electrical device is to pass electrical current from a stationary contact to a moving contact surface, or vice versa. Brushes and brush holders may be used in electrical devices such as electrical generators, electrical motors, and/or slip ring assemblies, or sliding connection applications, for example, slip ring assemblies on a rotating machine such as a rotating crane, a wind turbine or a linear sliding connection on a monorail. Brushes in many electrical devices are blocks or other structures made of conductive material, such as graphite, carbon graphite, electrographite, metal graphite, or the like, that are adapted for contact with a conductive surface or surfaces to pass electrical current.
In some designs, a box type brush holder is used to support the brush during operation. The brush and box are designed such that the brush can slide within the box to provide for continuing contact between the brush and the conductive surface contacted by the brush. Typically a spring, such as a constant force spring, presses against the upper surface of the brush to maintain contact between the lower surface of the brush and the conductive surface. Such springs are conventionally fixedly attached to a spring clip or a portion of the brush box such as with a rivet, weld or solder, thus not readily replaceable.
During the duration of operation of the electrical device, the brush will be reduced in size, or get shorter (i.e., diminish in longitudinal length), for example, as the wear surface of the brush in frictional sliding contact with the conductive surface wears down. Once a brush has worn beyond a threshold amount, the brush and/or other components may need to be replaced and/or maintenance may need to be performed.
A number of different brushes and brush holder structures, assemblies, and methods are known, each having certain advantages and disadvantages. However, there is an ongoing need to provide alternatives.